Semiconductor integrated circuit devices (ICs or “chips”) have to be tested for quality control as part of the manufacturing process. Automatic test equipment (ATE) are used to insert each chip (the “device under test” or DUT) into test sockets for testing. The ATE and their components are expected to last many thousands of test cycles. Any reduction in the cycle time due to equipment failure will contribute to increased costs for the manufacturer.
In addition, the ATE must not damage the chips in the testing process and an otherwise functional IC will be not be usable. This will also contribute to increased cost of manufacture.
During testing, proper electrical contact must be established and maintained between the leads of the DUT and the contacts of the test socket as this will affect the reliability of the test equipment to pick out faulty chips and not reject otherwise functional chips. Thus, this requirement of maintaining good electrical contact places demands on both the leads of the DUT and the test contacts used.
Now, metals are electrically conductive and the choice of the metal for use in the leads of a chip is a balance between cost, conductivity and suitability for use. Most metals are also subject to oxidation or corrosion and leads are usually plated to maintain electrical conductivity by preventing corrosion. Plating of leads also increases the hardness and wear resistance of the base metal and improves solderability at installation of the chip in a device.
Two main kinds of contacts are commonly used in ATE: straight “pogo” contacts with internal coil springs and bent cantilever contacts. The cantilever contact is exemplified by the invention by Yamaichi Electric Manufacturing Company and protected by a U.S. Pat. No. 4,997,378 (FIG. 1A).
In both kinds of contacts, a resilient means, be it the coil spring of the pogo contact or the loop of the cantilever contact, maintains a contact force against the lead of the chip to ensure good electrical contact. For unplated leads, it is desirable for the contact force to be large enough to allow the contact to break through a film of metal oxide on the lead. The contact may also be designed to permit a “wiping” action upon insertion of the DUT into the socket to scrub off this oxide film at the contact interface.
While this penetration or removal of the oxide film is desirable in unplated leads used in semiconductor chips of the past, this is not ideal for newer, plated leads as it will affect the solderability of the leads.
As the cantilever contacts of the prior art are designed to break through oxide layers, these contacts will also abrade the plating of these newer leads, affecting the quality of the soldering. The connection of the leads to the device in which the chip is installed will thus not be good. As such, an overly strong contact force by the contact of the ATE test socket is not desirable or suitable for chips with plated leads.
In addition, cantilever contacts of the prior art also do not have a long service life and must be cleaned and changed frequently.
Therefore, a need clearly exists for a contact that permits good electrical conduction between the lead of a device under test, with the test socket of automated test equipment, without compromising any plating on the lead as well as possessing a longer service life.